It doesn’t make any sense. If I make a box with a screen that runs linux (idk for ordering lunch in school canteen) and only update the OS by physically removing the hard drive and installing it from different computer, does that justify it being proprietary?

On the other end a circuit can be changed e.g. by tuning a potentiometer or straight up changing a component. That’s not any different than changing a value of a variable in the firmware. There is no actual difference in hardware and software, just different level of abstraction like C vs Python.